Five experienced electron microscopists belonging to the same department submit a proposal to replace two outdated electron microscopes with a new instrument. All investigators heavily rely upon electron microscopy in their research activities. These include studies on: 1. Processing of visual information by the mammalian retina: retinal neurons are penetrated by microelectrodes, their light responses are recorded, and, after intracellular delivery of an ultrastructural tracer, their synaptic connections are studied with the electron microscope. The electric signals generated by each individual cell are thus correlated to its inputs and outputs. 2. Molecular structure of gap junctions and tight junctions: the electron microscope is used in a morphological assay for the purity of the junctional preparations, to localize junctional epitopes in situ using immunocytochemistry and, finally, in combination with X-ray diffraction, to determine the molecular structure of gap junctions to atomic resolution. 3. Role of extracellular matrix (ECM) in morphogenesis: the electron microscope is used to analyze the interaction of the cytoskeleton with ECM and the induction by ECM of epithelial- mesenchymal transformation. 4. Process of damage and repair of the gastric mucosa: the electron microscope is used to study the mechanism of repair after injury and the effects of experimental maneuvers that favor the restoration process. The investigators are presently using two fifteen year old microscopes that need continuous repairs and have long breakdown periods; the moment is near that they will come to a complete halt. They would like to substitute for them a new, all-purpose, transmission electron microscope, that combines a routine high resolution performance with great speed in obtaining micrographs at low magnification.